An infrared welder for thermoplastic materials comprising the combination of a halogen lamp producing illumination in the infrared band located at the focal point of a first parabolic reflector. The parabolic reflector is joined in a substantially continuous fashion with a non-imaging lower reflector such as a Winston cone or a "CPC" having a lower aperture through which essentially all of the radiation from the source is directed. The aperture defines the shape and size of the weld area. The lower reflector may be brought into contact with the thermoplastic materials during the welding operation. Alternatively, a selectively operable press device may be used. Several embodiments are disclosed including embodiments which produce circular spot welds, linear welds, curved welds and corner welds.